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    Contrasting morphological responses to a singular flood event in neighbouring rivers and the implications for river management : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Geography at Massey University, Manawatū, New Zealand
    (Massey University, 2023) Coulston, Ethan James
    Geomorphic response to flood events is spatially and temporally variable and is influenced by many natural and anthropogenic processes. Research in recent times has shown the adverse geomorphic effects of rivers that have been managed by straightening, narrowing, and disconnecting them from their floodplain. This work attempts to evaluate the morphological response of small, rural gravel-bed rivers to discrete flood events and to put this response into the context of decadal-scale channel adjustments and river management practices. The Tauanui and Turanganui Rivers in South Wairarapa, New Zealand, were monitored and analysed to identify sediment dynamics within them and how they respond to discrete flood events and river management practices. This was achieved by analysing existing historic aerial and satellite imagery, cross-sectional survey data, and geomorphic change analyses using Structure from Motion (SFM) photogrammetry datasets collected in this project. Historical aerial imagery revealed that both rivers have significantly changed over time, with the area of active gravels reducing 38% in the Tauanui and 48% in the Turanganui River from the 1940s to 2013. A narrowing and straightening of both rivers and a proliferation of heavily vegetated banks was observed. It is suggested that these changes are linked to river management strategies, which have helped to develop floodplains for agriculture and occupation by people. Following a storm event on the 20th of June 2021, flooding caused significant geomorphic change. Geomorphic change analysis before and after suggested net aggradation of 1,564 m³ in the Tauanui River and 3,430 m³ in the Turanganui River. Although geomorphic change was significant in both study reaches, it contrasted. This contrast has been interpreted as a result of differences in river resilience and geomorphic thresholds. Similar to other studies, it is suggested that river management interventions have reduced resilience and brought both rivers closer to geomorphic thresholds. This has resulted in geomorphic change that is disproportionate to the flood magnitude. River management that homogenises river corridors is also detrimental to habitat diversity and increases the exposure of the surrounding land to flood risk.
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    Assessing the value of a geomorphic toolbox to assist with determining ecological health of wadable streams within the Waikato Region : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Geography at Massey University, New Zealand
    (Massey University, 2020) Lepper, Teryll Alexandra
    Ecological measures such as quantification of taxa and chemical indicators are well established as tools for assessing river health, but the geomorphic component is often left out despite forming the template on which all other processes occur. To address the missing geomorphic component in monitoring river health, this research focused on framing river health within a geomorphic context and formulated a Waikato Region-specific geomorphic toolbox to be integrated with existing river health monitoring, providing a more holistic understanding of rivers in the region. Six indicators were chosen to assess geomorphic condition and develop a toolbox: riparian zone, wood, bank erosion, particle size, connectivity and geomorphic units. Reference conditions were established for each site based on ‘minimally disturbed’ conditions. Qualitative and semi-quantitative techniques for assessing each indicator were outlined and tested against six monitoring sites – four ecological reference state and two non-reference state – within the Waikato Region using desktop based ‘apriori’ methods, as well as in-field monitoring. Assessment outputs included a qualitative proforma of each stream and a scoring mechanism to provide comparable results of each streams. Streams were given an assessment level from ‘Excellent’ to ‘Very Poor’ depending on their geomorphic quality. Four reference sites were assessed as ‘Excellent’, while the two non-reference sites were assessed as ‘Poor’ for geomorphic quality. Comparisons to ecological monitoring data of the same reaches showed a relationship between ecological and geomorphic health, such as the excellent fish and MCI scores corresponding with ‘Excellent’ geomorphology. However, proximity to the coast can skew fish indicators due to the diadromous nature of many native New Zealand fish; whilst the Whangarahi Stream was considered ‘Poor’ for geomorphic health, it was inhabited by an order of magnitude more eels than any other reach assessed. The use of reference conditions is integral to a well-functioning geomorphic toolbox, although further exploration is needed around whether reference conditions should represent ‘minimally disturbed’ or ‘best attainable’ condition given existing land use patterns. Inclusion of more encompassing geomorphic unit indicators, as well as bed structure would strengthen the toolbox. The geomorphic toolbox was created to provide meaningful and comparable data for assessing geomorphic health in a time- and cost-efficient manner, which has been achieved. Subject to further testing and refinement of variables to maintain relevance to a range of geomorphic contexts, the toolbox is considered adequate for inclusion into State of the Environment reporting structures for the Waikato Region.
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    The hydrogeology of the Pourewa sub-catchment, Rangitikei, New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Earth Science at Massey University, Palmerston North, New Zealand
    (Massey University, 2020) Rees, Callum
    This story begins in the geologically young and active landscapes of the lower North Island of New Zealand, positioned astride the interface between the Pacific and Australian tectonic plates. The chosen field area is located within the onland Whanganui Basin, a Late Miocene-Quaternary marine basin that has undergone uplift, inversion and fluvial incision to form spectacular river valley exposures through the basin succession. The area contains one of the most complete records of Quaternary climate change exposed onland anywhere in the world. Our journey centres on a portion of this uplifted marine basin, characterised by the highly erodible, pastorally farmed hill country of the Rangitikei. The Pourewa Stream, a tributary of the Rangitikei River provides a cross section through rural landscapes of the lower North Island. The stream’s headwaters begin in steep Taihape sheep and beef country, before transitioning into a broad valley with a gentle gradient headed for Hunterville. The lower reaches step down across extensive Late Pleistocene river terraces, providing versatile arable cropping and dairy pasture, until finally joining the Rangitikei River 6 km east of Marton. Agriculture constitutes 90% of land use in the region, placing pressure on resources required for ongoing agricultural development and production. Recent concerns surrounding the long-term sustainability and potential contamination of freshwater resources have initiated research into the regions groundwater system. Previous studies have taken a broad approach examining large-scale issues surrounding classification, allocation, management and vulnerability of groundwater resources. This study takes a different approach by examining a single sub-catchment of the Rangitikei River, with the aim of developing a conceptual hydrogeological model for the Pourewa Stream area. The proposed model is underlain by a comprehensive stratigraphic investigation of the Quaternary succession in the central Rangitikei. Geological context is provided through the development of a 1:25 000 geological map series and accompanying structural interpretation. Hydrogeochemical datasets derived from targeted in situ and laboratory based analysis provide baseline information. The conceptual hydrogeological model is applied on a wider regional scale to investigate basin history and processes of landscape formation. The project aims to support policy makers, landowners and developers in achieving sustainable management of groundwater resources by the avoidance of over exploitation and contamination.